Precipitated Calcium Carbonate Pigment, Especially for Use in Inkjet Printing Paper Coatings

ABSTRACT

Novel and innovative PCC pigments, having a reduced production cost, able to be used in a paper coating formulations to manufacture coated high-quality matt papers, in particular for inkjet applications. Process for the preparation of same, using a reduced flow rate of a carbon dioxide-containing gas in the PCC carbonation step, which produces stable, porous, agglomerates of PCC featuring unique properties and structure, this step being followed by an upconcentration step to increase the solids content.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to novel mineral pigments of theprecipitated calcium carbonate species (PCC).

More specifically, the invention relates to novel and innovative PCCpigments, able to be used in a paper coating formulations to manufacturecoated high-quality matt papers, in particular for inkjet applications,whose print qualities would be identical to commercially-availablecoated high-quality matt inkjet papers, but coated using pigments havinga reduced production cost.

The invention also relates to the production of said novel mineralpigments of the PCC species in slurry form, present in a solids contentappropriate for inkjet paper coating on a coater such as a Varibar™,airknife, curtain or blade off-line coater.

TECHNICAL PROBLEMS

There exists a demand for coated high-quality matt papers, and inparticular for papers suitable for inkjet applications, which lead toequal print quality relative to commercial papers of the same grade, butwith a lower associated production cost.

Traditionally, high-quality matt inkjet papers have been coated withexpensive fumed or precipitated silica, which adds considerably to thepaper cost.

One of the main hurdles to achieve an increase in print quality is toincrease the optical density of the ink applied to the paper surface, inparticular following full colour spectrum dye ink application.

Inkjet printers form images by applying a series of ink dots on thepaper surface. The dye inks used in inkjet printing are generallyanionic and in a low solids formulation that is naturally very mobile.Good print quality is only obtained if the ink dye remains on the papersurface as the ink solvent penetrates into the paper, leaving a uniformcircular dot at the point of application.

It is known that a charge difference between adsorbent and adsorbate,respectively the paper surface and the dye molecules, is generally usedto promote dye adsorption.

Hence, one solution to increase optical density lies in increasing thenumber of cationic sites near the paper surface. If the paper surface iscoated, the number of cations present near the surface can be increasedby adding cationic additives to the coating formulation. However, addingcationic additives in order to obtain a given optical density addssignificantly to the final paper cost.

Increasing the fraction of cationic additive retained in a thin layernear the paper surface, characterised by the coating holdout, is asecond solution to increase optical density. Higher coating holdout canbe achieved through the use of a narrower coating particle sizedistribution, which is a technically difficult and expensive solution.

If PCC is present in the coating formulation, the inherent adsorptiveproperties of PCC particles towards ink dyes can offer anotheralternative to reduce the quantity of cationic additives necessary toensure a given optical density. For an equal quantity of this pigment,decreasing the primary PCC particle size increases thepositively-charged pigment surface area available to interact with andbind ink dye. This promotes ink dye adsorption on the PCC particles nearthe site of ink application, which leads to an increase in opticaldensity.

Segregation of large dye molecules on the paper surface is also aided bysurface size exclusion and a high pore volume coating, allowing thepassage of solvent into the base paper while retaining the dye moleculeson the surface. This suggests the need for a porous coating formulation;one theoretical solution is therefore to introduceaggregates/agglomerates, such as possibly aggregated/agglomeratedpigments, in the coating formulation, with a carefully controlled poresize distribution and capillarity. However, as the skilled man knows,such a theoretical solution is quite difficult to specifically engineer;in the specifically related domain, U.S. Pat. No. 5,750,086 (discussedherebelow) produces finely divided PCC, along with numerous otherpatents, but not porous products or aggregates/agglomerates.

A second challenge in increasing print quality is to reduce the bleedingphenomenon observed following ink application to the paper surface. Inkdye bleeding of one colour into another adjacent colour occurs as aresult of latent ink dye binding to and drying on the paper surface, andis partly due to delayed ink solvent absorption into the base paper,which serves to bring the ink dye in contact with the surface for rapidbinding. Bleeding has as a consequence that printed images are distortedand appear less sharp.

Similarly, feathering also results in blurred images and occurs whendeposited ink follows the contours of the paper. As with ink bleeding,it is rectified by rapid ink drying, preferring dye absorption toadsorption when using porous media.

As the above implies, there is a need to balance and control inkadsorption onto the pigment surface as opposed to absorption into thevoid volume of pigment pores, since high absorption leads to decreasedbleeding and feathering, but with an accompanying decrease in opticaldensity, whereas high adsorption leads to improved optical density,while increasing bleeding and feathering.

A third challenge in obtaining a high print quality is to decrease theprint unevenness in the final paper product. Print unevenness is theresult of the inhomogeneous penetration of the ink-binding elements(cationic additive or coating pigment) of the coating formulation intothe base paper. Coating formulations having a low solids content presentan increased risk of solvent entraining the ink-binding, elements awayfrom the paper surface during two phenomena: as the formulation solventpasses into the base paper following paper coating and during the latermovement of the solvent to the paper surface during drying. Such surfaceunevenness can be limited by using a slurry presenting a high solidscontent, which limits the quantity of solvent passing into and out ofthe base paper. However, such a high solids content in incompatible withsome of the above objectives or theoretical solutions.

The above-listed constraints suggest the need for fixation of dyes onsites distributed homogeneously over the paper surface. It is clearlyimportant that the coating formulation be high in solids, however as isknown in the art, upconcentration of aggregate-containing slurries oftenlead to a loss of important pore volume.

As such, the theoretical solutions to the above-listed problems were notrecognized as able to solve the defined problems, and said list to thecontrary suggests that they must be delicately weighted and thatextremely difficult compromises, if not impossible ones, would have tobe found; this was nevertheless one of the objectives of this invention,and it is the merit of the invention to have ultimately reached a globalsolution. A second concern of the man skilled in the art is to achievethis balance employing a cost-efficient solution. Any skilled man willappreciate that such a requisite is always a factor highly complicatingthe definition of a technical solution, especially in the considereddomain.

Known multipurpose inkjet papers are characterized by surface sized orslightly pigmented qualities and generally surface sized or coated on acost-efficient on-line coater, such as the Metered Size Press (MSP) orFilm Press, allowing a high coating application speed and coating alower coat weight than their off-line-counterparts.

Speciality grade inkjet papers are characterized by a superiorhigh-resolution print quality relative to multipurpose papers. Suchpapers are generally coated at a high coat weight with formulationsincluding special high quality binders and additives via more costlycoating techniques, employing for example Varibar™, airknife, curtain orblade off-line coaters.

Due to raw material cost, production rate, coating weight andcomposition and coater type, the cost of a known multipurpose inkjetpaper is inferior to the cost of a high resolution matt inkjet paper byan order of magnitude which is roughly 6′ to 20 times. Hence, the manskilled in the art recognises the benefits of being able to obtain ahigh quality paper coating using a low cost coating solution.

As mentioned above, lowering the cationic additive demand of the coatingformulation, relative to current specialty pigments for inkjet, is alsodesirable for cost savings.

Further, it is of interest to reduce the quantity of binder needed,since this component represents an expensive part of the coatingcomposition and its presence on the paper surface decreases the activearea available to interact with ink. One option is to useaggregates/agglomerates presenting appropriately small pores, in whichcase only sufficient binder to adsorb onto the surface of theaggregates/agglomerates need be added, since the binder cannot attainthe surface of the primary particles exposed within the pores. However,as indicated above, this proposal is uniquely theoretical.

As regards the paper coating process, cost reduction can be attained bypromoting a more rapid paper drying step following coating. More rapiddrying translates to a higher paper machine speed and increasedproductivity since the risk of wet coating material deposits on thepaper-making machine is reduce. More rapid drying is possible throughthe use of a maximum solids content coating formulation.

A high solids coating formulation also reduces the cost associated withtransporting said coating formulation from the pigment manufacturer tothe paper mill, respectively coating plant.

A final concern of the man skilled in the art is to ensure an equal orimproved runnability (number of sheets produced without failure) oncoating machines such as the Varibar or airknife. It is known that thesecoaters demonstrate an improved runnability when using an increasedcoating slurry solids content, while maintaining a low (500 to 1500mPAs) slurry viscosity.

As the skilled man will appreciate, these are additional technicalproblems to be solved. The skilled man will also recognise that many ofsaid problems call for conflicting or antagonist solutions, which leadto severe problems if not properly balanced; this was the difficultproblem solved by this invention.

As mentioned above, the overall technical problem, and technicalchallenge, is to develop a novel class of PCC pigments structured to beused in a paper coating process to manufacture a paper which is“technically speaking” a coated high-quality matt paper, in particularfor inkjet applications, but at lower cost relative to other coatedpapers of the same grade, while maintaining print quality.

Last but not least, the solution must of course fit to as many types ofprinters as possible, if not all, adding another complexity to resolve.

Any skilled person will recognize both the commercial need for such aninnovative technology, the paramount technical challenge it represents,and the considerable technical, commercial and financial advance itwould bring.

PRIOR ART

Pigment options for use in high quality inkjet paper coatings currentlyon the market include specialty PCC inkjet pigments, such as those of EP0 815 174, or expensive fumed or precipitated silica.

Besides its considerable cost as a coating material, it is know thatsilica is generally limited to low solids coating formulation, whose useconsiderably reduces the coating line speed, further increasing tooverall coating cost. The man skilled in the art is therefore motivatedto seek lower cost coating alternatives available in higher solidsformulations.

According to EP 0 815 174, which relates to coating a PCC, anorganophosphonate compound, such as an amine-containing phosphoric acidor ethanol amine bis-(methylenephosphonic acid), is added to a PCCslurry in a quantity corresponding to 0.4 to 0.85% by weight relative tothe weight of PCC. Said slurry is then heat aged over a sufficient timeperiod (1 to 10 hours at a temperature exceeding 75° C., or 2 to 5 hoursat 80 to 85° C.) to impart a specific surface area exceeding 60 m²/g.

Alum or other inorganic, aluminium-containing compounds can beco-precipitated during the synthesis of PCC. In Example 1 of thispatent, addition of aluminium sulphate octadecahydrate is performed justprior to the carbon dioxide introduction. Optionally, up to 10% byweight of hydrated aluminium sulphate can also be introduced.

The heat ageing and/or milling of the PCC are regarded as critical inorder to reach an appropriate level of ink binding to the PCC.

To the contrary, as will be seen below, neither expensive,time-consuming heat ageing nor milling are required in the presentinvention; indeed, in the present invention, heat ageing even results inan inadmissible loss of PCC surface area.

EP 1 246 729 is presented as an improvement over the above mentionedpatent, and the product of this patent is said to feature a surface areaof 60 to 65 m²/g, preferably 80 to 90 m²/g, and generally no more than95 to 100 m²/g. That surface area is said to be obtained by heat ageingin the presence of an organophosphonate compound, as indicated above.The PCC particles are said to be individually spherical in shape, with adiameter of the order of 0.02 to 0.03 μm. This high specific surfacearea PCC presenting a narrow particle size is obtained in a 25% solidsslurry.

The alleged innovation in EP 1 246 729 comes from the combination of afinely divided PCC, presenting a surface area exceeding 60 m²/g, in amajor proportion, and a minor proportion of a gel-type silica, alongwith a binder.

The resulting composition can be blade coated, or less preferably coatedusing an air knife and Meyer bar.

The required presence of expensive silica represents a major drawback inthis patent.

U.S. Pat. No. 5,750,086 describes a process for manufacturing ultrafineparticles of colloidal calcium carbonate (PCC), in which magnesiumsulphate is added to a 3 to 14% by weight aqueous suspension of calciumhydroxide, followed by carbonation with the introduction of zincsulphate alone or together with sulphuric acid.

In the examples, the introduced metal salts solutions or sulphuric acidhave a concentration of 10% by weight.

The process is said to lead to chain-structured ultrafine particles ofcolloidal calcium carbonate having an average diameter of 0.01 μm ofsmaller, an average length of 0.05 μm or smaller, and a BET specificsurface area of 70 m²/g or greater.

The obtained ultrafine particles are said to “show lower affinity ofaggregation”. Indeed, the applicant primarily targets applicationsrequiring non-aggregated fillers, such as plastic applications whereinthe dispersibility of the end product is important. The presentinvention, by contrast, targets an aggregated/agglomerated product forinkjet paper applications.

The specific gas flow rate of 120 litres per minute per kilogram calciumhydroxide as indicated in the U.S. Pat. No. 5,750,086 examples, however,is quite significantly higher compared to the process conditions of thepresent invention, as will be seen herebelow.

Indeed, it was found according to the present invention and contrary tothe teaching of the prior art and common knowledge, that by decisivelyreducing the specific gas flow rate to below about 30 or below about 20litres per minute per kilogram calcium hydroxide during precipitation,one obtains not the discrete pigment described in U.S. Pat. No.5,750,086, but rather coarse mechanically stable porous sphericalagglomerates/aggregates consisting of said colloidal calcium carbonate.

As mentioned above, while it was possible to theorize regarding thepotential interest of porous PCC with an appropriate pore sizedistribution, possibly obtained via an agglomeration process, thisremained theoretical until the above surprising innovation. It has alsoto be noted that there is no indication whatsoever in the prior art orin the common knowledge that altering one parameter among dozens in thePCC preparation process, would lead to porous agglomerates. There iseven less indication that those agglomerates would be stable. There isstill less indication that the parameter to be modified was preciselysaid flow rate.

The process of U.S. Pat. No. 5,750,086 was reproduced with the abovemodification to the gas flow rate and the obtained product propertiesare shown in Table 2, Example 1.

As can be seen in Table 2, the product obtained by altering the teachingof U.S. Pat. No. 5,750,086 according to the invention is, quitesurprisingly, not the discrete pigment described in U.S. Pat. No.5,750,086, but rather coarse aggregates/agglomerates.

However, a problem with the slurry produced in Example 1 is the lowsolids content which is useful in many applications in the consideredindustries, but is not suitable for high quality paper coating. Thisrepresented an additional problem to be solved, as will be seenherebelow.

This surprising result is one of the key starting points of the presentinvention.

ADDITIONAL PRIOR ART

Japanese patent 2004-299302 teaches an inkjet record form featuring an“ink acceptance layer”, said layer comprising calcium carbonate as aprincipal pigment, which leads to improved feathering and bleeding.There is no specific indication as to the properties or structure ofsaid calcium carbonate to be used. This document instead focuses on theuse of a dispersant and the cationic charge density of said dispersant.

EP 0 761 782, Japanese patent 10-265 725 and Japanese patent 2004-197055 each describe improved inks for inkjet printing, namely used toimprove optical density, bleeding and/or feathering upon printing. Noneof these patents give a specific indication as to the coating pigment tobe used when preparing the paper sheet.

US 2003/0227 531 A1 discloses a paper coating of a polyvalent metalsalt, such as calcium, magnesium or aluminium onto one surface of thebase paper, in order to improve feathering and bleeding.

SUMMARY OF THE INVENTION

The objectives of the invention can only be fully reached by thecombination of the specific process for preparing porous, stable,agglomerates of PCC, using a decisively reduced gas flow rate for thecarbonation step, and of the selected upconcentration steps to produce ahigh solids PCC slurry suitable for inkjet paper coating applications.

It is briefly reminded here that PCC is generally obtained in the priorart via the following steps: a calcium hydroxide slurry at about 13%solids is first prepared by slaking; calcium oxide (also referred to asburnt lime or quicklime) is mixed with water in a stirring reactor ortank. Said calcium hydroxide slurry is then screened, such as on a 100μm screen, to remove any residual impurities and/or non-reactive unburntlime, and then directed towards a stainless steel reactor equipped withan agitator. The temperature is adjusted, generally to around 20° C.,and then the slurry is directed towards the carbonation reactor or tankwhere carbon dioxide is bubbled through, optionally with air,precipitating PCC. The PCC slurry leaves the carbonation tank whenappropriate in view of an appropriate drop in pH and/or conductivity.

The above is known to the skilled man, and the following patents areincorporated herein by reference: EP 0 768 344, WO 98/52870(PCT/US98/09019) and WO 99/51691 (PCT/US99/07233).

Generally speaking, the present invention resides in a series of firststeps (Steps A) leading to the production of a low solids PCC slurry,comprising essentially porous, stable, agglomerates/aggregates of PCCparticles, followed by the upconcentration of said slurry (Steps B)without loss of said agglomerates/aggregates.

Steps A of the invention relate to a process for the preparation ofporous, stable agglomerates/aggregates of PCC as a low solids slurry,and the so-obtained PCC product, which is a new industrial product.

The invention therefore covers a new process for producing a PCC slurryvia the carbonation route, characterized in that the carbonation step isconducted with a carbonation gas flow rate decisively reduced to below30 litres per minute at standard temperature and pressure per kilogramcalcium hydroxide during precipitation (Steps A).

The present invention also covers a new process for producing a PCCslurry via the carbonation route, additionally characterized in that theproduction of PCC as described in the above paragraph is conducted inthe presence of magnesium sulphate, in combination with one or moregroup II or III metal sulphates, said metal sulphate(s) being inparticular aluminium based and/or zinc based, preferably aluminium basedor zinc based. These steps are based on those described in U.S. Pat. No.5,750,086, however with the much lower carbonation gas flow rate asmentioned above.

The surprising result is that the pigment obtained is not anon-agglomerating, ultrafine particular, discrete product, but rathercoarse (1 to 5 μm range) porous and stable agglomerates/aggregates.

The produced agglomerates/aggregates are surprisingly so stable thatthey are substantially maintained in agglomerated/aggregated form duringa subsequent “upconcentration” step, and astonishingly the finallyproduced PCC agglomerates/aggregates impart equal print properties whenincorporated in high-quality matt inkjet paper coatings, as compared tothe print quality of other market papers of higher production cost.

In most preferred embodiments, Steps A of the present invention areadditionally characterized by the use of the inventive combination ofmagnesium sulphate and aluminium sulphate, or magnesium sulphate andzinc sulphate.

In less preferred embodiments, the process of the invention uses thecombination of magnesium sulphate and zinc sulphate, to which is addedaluminium sulphate, or the combination of magnesium sulphate andaluminium sulphate, to which is added zinc sulphate. Further, a lesspreferred embodiment includes the use of magnesium sulphate and one ormore sulphates of group II and/or III metals.

The invention additionally lies in the combination of the PCC productionprocess (Steps A), with subsequent particular upconcentration(dewatering/redispersion) steps without dispersant or in the presence ofa cationic dispersant (Steps B).

It is entirely innovative to use the combination: PCC production (StepsA) with the upconcentration process (Steps B) for this type of inkjetapplication.

The final product is, quite surprisingly, a PCC in the form of stableagglomerates/aggregates having an average diameter in the μm range,namely between 1 and 5 μm, forming a PCC pigment which, when used in astandard high quality matt inkjet coating formulation, leads to a equalor similar print qualities at reduced cost.

The invention also covers novel PCC pigments per se, as new industrialproducts, in the form of stable agglomerates/aggregates in the μm range,namely between 1 and 5 μm, as obtained at the end of Steps A or at theend of Steps A and B. This is entirely different from the commercialtechnologies and prior patents.

The invention also covers the novel pigment slurries containing saidpigments as new industrial products, namely the low solids slurryobtained at the end of Steps A and the high solids slurry obtained atthe end of Steps A and B.

The invention additionally covers novel coating formulations for coatingink jet paper containing said pigments or pigment slurries

The invention also covers coated ink jet papers, coated with such novelcoating formulations.

DETAILED DESCRIPTION OF THE INVENTION

The invention relates to:

-   -   a process for providing PCC useful for ink-jet printing        applications,    -   of the type according to which a calcium hydroxide slurry is        first prepared by mixing quicklime (CaO) with water in a        stirring reactor or tank (“slake”). The calcium hydroxide slurry        is then screened, such as on a 100 μm screen, to remove any        residual impurities and/or non-reactive unburnt lime. The        screened slurry is then directed towards a stainless steel        reactor equipped with an agitator; the temperature is adjusted,        generally to between 10 and 70° C., and subsequently the slurry        is directed towards a carbonation reactor or tank, wherein        carbon dioxide-containing gas is bubbled through the slurry. The        slurry exits the carbonation tank when appropriate in view of        conductivity and pH, generally when the conductivity reaches a        minimum and the pH drops below 8. Coarse particles are removed        on a screen, such as a 45 μm screen, such that the slurry        contains only the ultrafine PCC agglomerates of the invention,    -   characterized by the implementation of process steps comprising        a series of first steps, relating to the production of the PCC        in which:        A1 In a PCC production process as described above, the        carbonation step is performed at a carbonation gas flow rate of        below 30 litres per minute at standard temperature and pressure        per kilogram calcium hydroxide during precipitation.

The invention also relates to a process as above, in which:

A2 In a PCC production process as described above under A1 or A2, theslurry of calcium hydroxide leaving said stainless steel reactor aftersaid separation of said residual impurities and/or non-reactive unburntlime is treated by a combination of magnesium sulphate and Group IIand/or Group III metal sulphates, most preferably in the presence of anacid, said acid being most preferably sulphuric acid, until stable,porous agglomerates/aggregates are obtained at a concentration of 5 to25% solids, preferably 15 to 20% solids (“precursor”).

The invention also relates to a process as above, in which:

A3 In a PCC production process as described above under A1, A2 or A3,the slurry of calcium hydroxide is first prepared by mixing quicklimewith water in a stirring reactor or tank (“slake”) in a weight ratio ofCaO:water between 1:3 and 1:20, preferably between 1:5 and 1:12, mostpreferably between 1:7 and 1:10.

The invention also relates to a process as above, in which:

A4 In a PCC production process as described above under A1, thetemperature is preferably adjusted to between 15 and 50° C., mostpreferably to between 15 and 30° C., before the slurry is directedtowards the carbonation reactor or tank.

These steps are schematically shown on attached FIG. 1. On said figure,the references have the following meanings:

I: Water II: Quicklime

III: Reactor, such as a stirred reactor or tankIV: Screen, such as a 100 μm screenV: Residual Impurities and/or Non-reactive unburnt Lime

VI: Calcium Hydroxide Slurry

VII: Reactor, such as a carbonation reactor or tank

VIII: Magnesium Sulphate Solution

IX: Group II and/or Group III Metal Sulphate(s)X: Acid, such as sulphuric acid

XI: Carbon Dioxide-Containing Gas

XII: Screen, such as a 45 μm screen

XIII: Coarse Particles

XIV: Invention PCC (in a porous, agglomerated form) Slurry

Steps A are followed by the upconcentration of the PCC produced duringSteps A, without dispersant or in the presence of cationic dispersant,under sufficiently gentle or mild conditions for theaggregates/agglomerates not to be substantially destroyed, until aconcentration, of 15 to 50%, preferably in the range 20 to 30%, mostpreferably 23 to 26% solids by weight is reached. The amount of anycationic dispersant added is controlled so that the PCCagglomerates/aggregates of the precursor are just coated, this quantitycorresponding that added prior to a slurry viscosity increase.

If the upconcentration leads to a filter cake, such as followingupconcentration performed using a pressurized filter, or a centrifuge,or by vacuum filtration, the concentrated material is optionally washedwith water and a redispersion is performed until the final materialsubstantially consists of stable, porous agglomerates/aggregatesidentical with or very similar to those obtained in Steps A.

The upconcentration can be performed in a thermal evaporation step withthe final material substantially remaining in the form of the stable,porous agglomerates/aggregates obtained in Steps A.

The upconcentration of part or all of the precursor may lead to a dryproduct, and in such a case, the dry product is redispersed until thefinal material substantially consists of stable, porousagglomerates/aggregates identical with or very similar to those obtainedin Steps A.

FIG. 2 represents a dewatering process in a centrifuge, with:

I: PCC slurry from Steps AII: Dewatering centrifuge

III: Filtrate IV: Filter Cake V: Dispersing Unit VI: Optional Additionof a Solution of a Cationic Dispersing Aid VII: Upconcentrated PCCSlurry

FIG. 3 represents an alternate dewatering process in a centrifuge, with:

I: PCC slurry from Steps AII: Dewatering centrifuge

III: Filtrate IV: Filter Cake V: Dispersing Unit VI: Optional Additionof a Solution of a Cationic Dispersing Aid VII: Upconcentrated PCCSlurry

FIG. 4 represents a thermal upconcentration step under vacuum, with:

I: PCC slurry from Steps A

II: Thermal Evaporator III: Upconcentrated PCC Slurry

FIG. 5 represents a thermal upconcentration on a heating plate, with:

I: PCC slurry from Steps A

II: Heating Plate III: Optional Addition of a Solution of a CationicDispersing Aid IV: Upconcentrated PCC Slurry

The following are optional and/or preferred features in Steps A, to betaken alone or in combination.

The carbonation gas flow rate is preferably selected in the range of 1to 30, preferably 10 to 20, most preferably around 19.7 litres perminute at standard temperature and pressure per kilogram calciumhydroxide during precipitation. Said carbonation gas is CO₂ or a mixtureof CO₂ and one or more other gases, such as air and/or nitrogen.

The slurry of calcium hydroxide is most preferably treated by acombination of magnesium sulphate and aluminium sulphate, or acombination of magnesium sulphate and zinc sulphate.

According to less preferred options, zinc sulphate can be added to thecombination of magnesium sulphate and aluminium sulphate, or aluminiumsulphate can be added to the combination of magnesium sulphate and zincsulphate.

The addition of magnesium sulphate is most preferably performed beforecarbonation. Magnesium sulphate can be added, in a less preferredoption, either before the addition of other sulphates or during thataddition. In a second, less preferred option, magnesium sulphate can beadded during carbonation along with aluminium and/or zinc sulphate. As aleast preferred option of the invention, magnesium sulphate can be addedduring carbonation or just at the beginning of carbonation.

The addition of aluminium sulphate and/or zinc sulphate most preferablytakes place over the period of carbonation.

The addition of the acid, namely sulphuric acid, most preferably in theform of a 10% by weight solution of sulphuric acid, takes placepreferably at the beginning of the carbonation. Most preferably,however, the addition of sulphuric acid takes place simultaneously withthe addition of aluminium sulphate or zinc sulphate.

Without being bound by any theory, the applicant is of the opinion thatin the present invention, the presence, as described below, of sulphuricacid is necessary for achieving proper results.

In all the above options, sulphates of Group II and/or III can be addedin addition to aluminium sulphate and/or zinc sulphate, or as asubstitute for aluminium sulphate and/or zinc sulphate.

The temperature in the carbonation tank is observed to rise up tobetween 40 and 80° C., preferably up to between 50 and 60° C., mostpreferably up to between 56 and 57° C.

Removal of residual impurities and/or non-reactive unburnt lime takesplace on a 45 μm mesh screen when the Brookfield viscosity of thematerial exiting from the carbonation tank is sufficiently low, namelyless than 100 mPas at 100 rpm.

The final slurry product substantially consists of stable, porousagglomerates/aggregates.

The following are optional and/or preferred features in Steps B, to betaken alone or in combination.

By “deagglomeration/deaggregation” it is meant that theagglomerates/aggregates obtained at the end of Steps A by the specificprocess of the invention are disintegrated, the disintegrated productbeing ultrafine PCC of the same kind (with the exception of thecontained or deposited metal salts) as the one obtained in USP'086.

By “gentle or mild conditions” it is meant that thedeagglomeration/deaggregation of the agglomerates/aggregates is kept toa minimum, so that said agglomerates/aggregates are not “substantiallydestroyed”. More precisely, this means that it is most preferred thatduring the upconcentration steps, the increase in the fraction ofparticles below 2 μm is limited to less than 30%, preferably less than20%, most preferably less than 10%, and/or the decrease of the meanaggregate diameter is limited to less than 20%, preferably less than15%, most preferably less than 10%, as measured according to the meansdescribed below.

SEM images before and after upconcentration are substantially identicalwhich means that the existing agglomerates/aggregates (as obtained inStep A “precursor”) are not noticeably altered during upconcentration.

The upconcentration step can be performed in the form of any thermal ormechanical separation technology for solid/liquid suspensions providedthe aggregates/agglomerates obtained in Steps A (“precursor”) aresufficiently stable and are not “substantially destroyed” by saidtechnology.

During the upconcentration process, a common cationic dispersant may beadded in the customary proportions, in order to increase the slurrysolids content without overly increasing the viscosity of the slurry.The amount of any cationic dispersant added is controlled so that thePCC agglomerates/aggregates of the precursor are just coated, thisquantity corresponding that added prior to a slurry viscosity increase.For example, approximately 3 to 15% w/w of a 20% solution of a cationiccopolymer, such as a cationic copolymer of[2-(methacryloyloxy)ethyl]trimethyl ammonium chloride and[3-(methacrylamido)propyl]trimethyl ammonium chloride, to dry calciumcarbonate is added to the slurry containing the pigment of theinvention, corresponding to approximately 0.6 to 3% weight dry cationicdispersant on dry calcium carbonate.

Most preferably, upconcentrations with a cationic dispersant or withoutdispersant are by vacuum filtration or by thermal upconcentration or bycentrifuge or by pressurised filter.

A degree of destruction of the agglomerates/aggregates was expected.Such pigment aggregates/agglomerates are often held together byrelatively weak Van der Waals or electrostatic attractive forces, whichare surpassed by the centrifugal and/or shear forces created within theequipment associated with commercial upconcentration, namely within thecentrifuge, fast-rotating decanter or high pressure filter press. Theresult that no noticeable destruction of aggregates/agglomerates isobserved while fully achieving the degree of required upconcentration istherefore entirely not obvious.

The present invention covers the stable, porous aggregates/agglomeratesof PCC produced at the end of Steps A alone (“precursor”), and the finalstable, porous aggregates/agglomerates of PCC, as obtained by the aboveprocesses, at the end of Steps A in combination with Steps B, said PCCfeaturing quite innovative properties which in turn make it ofparticular value for ink-jet applications.

The stable, porous aggregates/agglomerates of PCC obtained at the end ofSteps A as well as those obtained after the upconcentration Steps B canbe characterized by a selection of the following: a specific surfacearea of 30 to 100 m²/g, preferably 50 to 80 m²/g, and/or a meanaggregate diameter of 1 to 5 μm, with an average diameter of 2 μm,and/or a fraction of fines below 2 μm of less than 20%, preferably ofless than 15%, and/or a primary acicular particle size of 20 to 50 nm,with an aspect ratio between 1:2 and 1:10, and/or a solids content, byweight from 5 to 25%, preferably 15 to 20% at the end of Steps A, and asolids content of 15 to 50%, preferably 20 to 30% solids, in particular23 to 26% solids at the end of Steps B.

The final slurry concentration may be partially or wholly obtained bythe addition of one or more additional pigments or pigment slurriesduring Steps B.

The invention covers the novel pigments characterized in that theycomprise stable, porous PCC aggregates/agglomerates as described herein,and novel pigment or PCC slurries characterized in that they comprisestable, porous PCC aggregates/agglomerates as described herein.

The invention also covers novel pigments and PCC slurries characterizedin that their solids concentration is, by weight, from 5 to 25%,preferably 15 to 20% solids at the end of Steps A, and from 15 to 50%,preferably 20 to 30% solids, in particular 23 to 26% solids at the endof Steps B.

According to a preferred embodiment, the functional pigment or pigmentslurry with a high surface area and integrated cations, is incorporatedin the coating formulation in a way known to the skilled man, in orderto increase namely the optical density upon printing without an increasein bleeding or feathering: this is one of the major achievements of theinvention.

The invention therefore also covers novel coating formulations for thepaper making industry characterized in that they comprise novelaggregates/agglomerates of PCC, novel pigments and/or novel slurriesdescribed herein.

The invention also covers coating formulations as described hereincharacterized in that the PCC slurry which it contains features thefollowing properties: a solids content of 15 to 50%, preferably 20 to30% solids, in particular 23 to 26%, and/or a high surface area PCC,namely featuring a specific surface area of 30 to 100 m²/g, preferably50 to 80 m²/g.

The invention also covers the applications of the coating formulationsaccording to any of claims 19 or 20 relating to the coating of inkjetpaper, namely to the coating of “multipurpose” inkjet paper or ofspecialty, high quality, paper.

To sum up, the most preferred (according to its best mode as of thisdate) invention relies on the selection of a reduced carbonation gasflow rate during the precipitation of the PCC, the specific combinationof cations introduced in the PCC crystal lattice during PCC synthesis,the use of a high solids coating slurry, upconcentrated with dispersantto 15 to 50%, preferably 20 to 30%, in particular around 23 to 26% byweight, in particular for use in paper coatings to be coated on Varibar,airknife or blade off-line coaters, the use a high surface area PCC inthe range of 30 to 100 m²/g, preferably 50 to 80 m²/g at the end ofSteps A and at the end of Steps B, the use of small diameter PCC primarycrystals, agglomerated/aggregated to form a porous PCC agglomerate.

As surface area is a function of particle size distribution, thisdistribution will have to be set accordingly.

The resulting functional pigment surface chemistry ensures an increasedink dye fixation and increased pigment surface area resulting inincreased optical density, or a lower cationic additive demand incoating formulation for an equal optical density. No increase or even adecrease in bleeding and/or feathering relative to commercialalternatives is observed.

The possibility of obtaining a high solids content slurry with theinvention pigment leads to better runnability when incorporated in apaper coating formulation and coated on base paper. The high solidscontent leads to less drying energy demand and easier and faster drying;a higher paper machine speed is possible without an increase in depositson the rolls in paper machine after-drying section.

The invention leads to a high solids content coating slurry meaning thatless energy must be introduced during the drying step, thereby reducingthe cost.

Further the use of the inventive aggregates/agglomerates limits thequantity of binder needed, thereby limiting cost.

Because the invention will favour agglomerates/aggregates, theapplications will be limited to matt inkjet paper applications. Theinvention agglomerates/aggregates are too coarse to obtain a glossyfinish.

Various processes of the invention will be better understood through thefollowing description and the following non-limiting examples.

EXAMPLES Examples of Preparations of the Innovative Inkjet Pigment andPigment Data for the Corresponding Products

Examples 1, 5, 7 and 10 were prepared according to Steps A of theinvention. Examples 2, 3, 4, 6, 8, 9, 11 and 12 were upconcentrations ofone of Examples 1, 5, 7 and 10, upconcentrated according to theinvention (Steps B).

Example 1

Process of the Invention, Steps a with Magnesium Sulphate and ZincSulphate

150 kg of quicklime were added to 1300 litres of tap water in a stirredreactor. Before lime addition the water temperature was adjusted to 40°C.

The quicklime was slaked for 25 minutes under continuous stirring andthe resulting slurry of calcium hydroxide (“milk of lime”) at 13.1% w/wsolids was then screened on a 100 μm screen.

The calcium carbonate precipitation was conducted to a 1000 litrebaffled cylindrical stainless steel reactor equipped with an gasingagitator having a gas dispersion unit, a stainless steel carbonationtube to direct a carbon dioxide/air gas stream to the impeller, andprobes for monitoring the pH and conductivity of the suspension.

700 litres of the calcium hydroxide suspension obtained in the slakingstep as stated above were added to the carbonating reactor and thetemperature of the reaction mixture was adjusted to the desired startingtemperature of 20° C.

Prior to carbonation, 30 kg of 10% w/w aqueous solution of magnesiumsulphate (MgSO₄.7H₂O) was added to the milk of lime.

The agitator was then adjusted to 1480 rpm, and the slurry wascarbonated by passing a gas mixture of 26 volume percent carbon dioxidein air at 118 Nm³/h, corresponding to 19.7 litres per minute at standardtemperature and pressure per kilogram of calcium hydroxide, through theslurry. During carbonation, 100 kg of 10% w/w aqueous solution of zincsulphate (ZnSO₄.7H₂O) and 30 kg of 10% w/w aqueous solution of sulphuricacid were added to the reaction mixture in a continuous manner over thetotal carbonation time.

Completion of carbonation was reached after 1 hour, 55 minutes reactiontime and indicated by a drop in conductivity to a minimum accompanied bya drop in pH to a constant value below 8.0.

During carbonation, the slurry temperature was allowed to rise due tothe exothermic nature of the reaction to a final slurry temperature of57° C.

The residual impurities and/or non-reactive unburnt lime was thenremoved by passing the aqueous slurry through a 45 μm screen.

The product of the above carbonation was an aqueous suspension of 15.6%w/w solids content of ultrafine primary calcium carbonate particlesbound together to form stable porous spherical aggregates.

The single crystals as constituents of the aggregates featured aparticle diameter of 20 to 50 nm and an aspect ratio between 1:2 and1:10 according to SEM pictures. The porous aggregates formed from thesesingle crystals showed diameters between 1 to 5 μm, with an averagediameter of 2 μm, also according to SEM pictures.

Pigment data of the product obtained in the process described above arelisted as Example 1 in Table 2.

The table results for Example 1 confirm the high aggregate surface areaand appropriate aggregate dimensions, but an insufficient solids contentfor subsequent coating applications. Indeed, the results of a coatingtrial with a low solids formulation run according to the general coatingconditions described hereafter, demonstrate that for an equal solidsaddition per paper surface area, coating with a lower solids formulationleads to a decrease in optical density (Table 1).

It is therefore necessary to upconcentrate without a noticeable loss ordegradation of aggregates.

TABLE 1 Effect of total slurry solids content on 100% black opticaldensity Total slurry Metal sulphate solids content in the total slurryMetal Sulphate 100% Black (% wt) solids (% wt) type optical density 13.710 ZnSO₄*7H₂0 2.44 36.7 10 ZnSO₄*7H₂0 2.72

Example 2 Process of the Invention, Upconcentration (Steps B) of theProduct of Example 1

2210 g of the precipitated calcium carbonate slurry obtained accordingto process Steps A as described in Example 1 were cooled to 25° C. anddewatered in Steps B using a pressurized filter.

One obtains a filter cake of about 43% w/w solids.

The filtrate was collected and used for redispersion of the filter cake.

50 g of filtrate obtained in dewatering step as described above wasadded in a 1 litre dispersing unit equipped with an impeller andredispersed without the use of any dispersant.

Into this mixture, the filtercake having 57% w/w residual moisturecontent, as obtained in dewatering step described above, was addedstepwise into the dispersing unit under continuous mixing.

After each addition of filter cake and subsequent homogenization, theslurry Brookfield viscosity at 100 rpm was determined. The addition offilter cake was stopped when the Brookfield viscosity reached a definedmaximum limit of approximately 1000 mPas.

At this point 97 g of filter cake had been added.

The product of the upconcentration process described above was anaqueous suspension with 28.4% w/w solids content ultrafine primarycalcium carbonate particles bound together to form stable porousspherical aggregates of 1 to 5 μm.

The crystalline structure of the product was determined by SEM pictures.

Pigment data of the product obtained in the process described above arelisted as Example 2 in Table 2.

From these data it can be seen that the obtained pigment features a highBET specific surface area value, which shows that one has obtained thehigh surface needed to interact and bind the ink, along with appropriateaggregate dimensions (1 to 2 μm according to SEM) and yellowing index.

The final product additionally features a sufficient solids content forsubsequent ink jet paper coating applications.

Example 3 Process of the Invention, Upconcentration (Steps B) of theProduct of Example 1

2210 g of the precipitated calcium carbonate slurry obtained accordingto the process described in Example 1 were cooled to 25° C. anddewatered using a pressurized filter. The filtrate was collected andused for later redispersion of filtercake.

30 g of filtrate obtained in dewatering step as described above wasadded to a 1 litre dispersing unit equipped with an impeller andredispersed without the use of any dispersant.

Into this mixture, filtercake having residual moisture of 36.4% w/wobtained in dewatering step described above was added stepwise to thedispersing unit under continuous mixing. After each addition of filtercake and subsequent homogenization, the slurry Brookfield viscosity at100 rpm was determined. The addition of filter cake was stopped when theBrookfield viscosity reached a defined maximum limit of approximately1000 mPas.

At this moment 49 g of filter cake had been added.

The product of the upconcentration process described above was anaqueous suspension with 22.5% w/w solids content of ultrafine primarycalcium carbonate particles bound together to form stable porousspherical aggregates.

The crystalline structure of the product was determined by SEM pictures.

Pigment data of the product obtained in the process described above arelisted as Example 3 in Table 2.

The results call for the same comments as in Example 2.

Example 4 Process of the Invention, PCC Production (Step A, OptionMagnesium Sulphate and Zinc Sulphate) and Upconcentration (Steps B)

150 kg of quicklime were added to 1300 litres of tap water in a stirredreactor. Before lime addition, the water temperature was adjusted to 40°C.

The quicklime was slaked for 25 minutes under continuous stirring andthe resulting slurry of calcium hydroxide (“milk of lime”) at 12.8% w/wsolids was then screened on a 100 μm screen.

The calcium carbonate precipitation was conducted to a 1000 litrebaffled cylindrical stainless steel reactor equipped with an gasingagitator having a gas dispersion unit, a stainless steel carbonationtube to direct a carbon dioxide/air gas stream to the impeller, andprobes for monitoring the pH and conductivity of the suspension.

700 litres of the calcium hydroxide suspension obtained in the slakingstep as stated above were added to the carbonating reactor and thetemperature of the reaction mixture was adjusted to the desired startingtemperature of 20° C.

Before the start of carbonation, 30 kg of 10% w/w aqueous solution ofmagnesium sulphate (MgSO₄.7H₂O) was added to the milk of lime.

The agitator was then adjusted to 1480 rpm, and the slurry wascarbonated by passing a gas mixture of 26 volume percent carbon dioxidein air at 118 Nm³/h, corresponding to 19.7 litres per minute at standardtemperature and pressure per kilogram of calcium hydroxide, through theslurry.

During carbonation 100 kg of 10% w/w aqueous solution of zinc sulphate(ZnSO₄.7H₂O) and 30 kg of 10% w/w aqueous solution of sulphuric acidwere added continuously over total carbonation time to the reactionmixture.

Completion of carbonation was reached after 1 hour, 50 minutes reactiontime and indicated by a drop in conductivity to a minimum accompanied bya drop in pH to a constant value below 8.0.

During carbonation slurry temperature was allowed to rise resulting in afinal slurry temperature of 58° C. due to the heat generated during theexothermic reaction.

Upconcentration Step:

The slurry was then screened on a 45 μm screen before being fed to adewatering centrifuge (operating at 4440 rpm) at a rate of 350 l/h. Nodispersant was added to the resulting filter cake. This filter cake wascollected and then redispersed in a mixing unit and the upconcentratedproduct was recovered as an aqueous slurry of the pigment.

Product of the carbonation and upconcentration steps as stated above wasan aqueous suspension of 19.5% w/w solids content of ultrafine primarycalcium carbonate particles bound together to form stable porousspherical aggregates. The single crystals as constituents of theaggregates had acicular particle shape with a diameter of 20 to 50 nmand aspect ratios between 1:2 and 1:10. The porous aggregates formedfrom these single crystals showed diameters between 1 and 5 μm, with anaverage diameter of 2 μm.

The crystalline structure of the product was determined by SEM pictures.

Pigment data of the product obtained in the process described above arelisted as Example 4 in Table 2.

The results call for the same comments as Examples 2 and 3.

Example 5 Process of the Invention, Steps A, Option Magnesium Sulphateand Aluminium Sulphate

115 kg of quicklime were added to 1000 litres of tap water in a stirredreactor. Before lime addition the water temperature was adjusted to 40°C.

The quicklime was slaked for 25 minutes under continuous stirring andthe resulting slurry of calcium hydroxide (“milk of lime”) at 12.7% w/wsolids was then screened on a 100 μm screen.

The calcium carbonate precipitate was conducted in a 1000 litre baffledcylindrical stainless steel reactor equipped with an gasing agitatorhaving a gas dispersion unit, a stainless steel carbonation tube todirect a carbon dioxide/air gas stream to the impeller, and probes formonitoring the pH and conductivity of the suspension.

700 litres of the calcium hydroxide suspension obtained in the slakingstep as stated above were added to the carbonating reactor and thetemperature of the reaction mixture was adjusted to the desired startingtemperature of 20° C.

Before the start of carbonation, 30 kg of 10% w/w aqueous solution ofmagnesium sulphate (MgSO₄.7H₂O) was added to the milk of lime. Theagitator was then adjusted to 1480 rpm, and the slurry was carbonated bypassing a gas mixture of 26 volume percent carbon dioxide in air at 118Nm³/h, corresponding to 19.7 litres per minute at standard temperatureand pressure per kilogram of calcium hydroxide, through the slurry.

During carbonation, 100 kg of 10% w/w aqueous solution of aluminiumsulphate (Al₂(SO₄)₃.18H₂O) and 30 kg of 10% w/w aqueous solution ofsulphuric acid were added continuously to the reaction mixture over thetotal carbonation time.

Completion of carbonation was reached after 1 hour, 48 minutes reactiontime and indicated by a drop in conductivity to a minimum accompanied bya drop in pH to a constant value below 8.0.

During carbonation, the slurry temperature was allowed to rise resultingin a final slurry temperature of 61° C. due to the heat generated duringthe exothermic reaction.

The slurry was then screened on a 45 μm screen and the product recoveredas an aqueous slurry of the pigment.

The product of the carbonation step described above was an aqueoussuspension with 14.3% w/w solids content of ultrafine primary calciumcarbonate particles bound together to form stable porous sphericalaggregates.

The single crystals as constituents of the aggregates featured acicularparticle shapes with a diameter of 20 to 50 nm and aspect ratios between1:2 and 1:10.

The porous aggregates formed from these single crystals showed diametersbetween 1 to 5 μm, with an average diameter of 2 μm.

The crystalline structure of the product was determined by SEM pictures.

Pigment data of the product obtained in the process described above arelisted as Example 5 in Table 2.

Example 6 Process of the Invention, Upconcentration (Steps B) of theProduct of Example 5

10 litres of the precipitated calcium carbonate slurry obtainedaccording to process described in Example 5 were screened on a 45 μmscreen prior to being fed to a thermal evaporator. The evaporatorconsisted of a cylindrical stainless steel vessel equipped with anagitator and a double mantle heating unit operating with 120° C. hotsynthetic oil as heating media.

Prior to evaporation 194 g of a 20% solution of a cationic copolymer of[2-(methacryloyloxy)ethyl]trimethyl ammonium chloride and of[3-(methacrylamido)propyl]trimethyl ammonium chloride, along with 10.8 gof Hydroxy Ethyl Cellulose (HEC, Tylose H6000YP2, an anti-settling agentfrom Clariant™) was added to the precipitated calcium carbonate slurryand mixed in.

Thermal upconcentration was achieved through evaporation in said labevaporator under atmospheric pressure at slurry temperatures rangingfrom 90 to 95° C.

The evaporation was stopped when the Brookfield viscosity reacheddefined maximum limit of approximately 1000 mPas.

The product of the upconcentration process described above was anaqueous suspension with 23.8% w/w solids content of ultrafine primarycalcium carbonate particles, bound together to form stable porousspherical aggregates.

The crystalline structure of the product was determined by SEM pictures.

Pigment data of the product obtained in the process described above arelisted as Example 6 in Table 2.

Example 7 Process of the Invention, Steps A (Option Magnesium Sulphateand Zinc Sulphate):

115 kg of quicklime were added to 1000 litres of tap water in a stirredreactor. Before lime addition the water temperature was adjusted to 40°C.

The quicklime was slaked for 25 minutes under continuous stirring andthe resulting slurry of calcium hydroxide (“milk of lime”) at 12.5% w/wsolids was then screened on a 100 μm screen.

The calcium carbonate precipitate was conducted to a 1000 litre baffledcylindrical stainless steel reactor equipped with an gasing agitatorhaving a gas dispersion unit, a stainless steel carbonation tube todirect a carbon dioxide/air gas stream to the impeller, and probes formonitoring the pH and conductivity of the suspension.

700 litres of the calcium hydroxide suspension obtained in the slakingstep as stated above were added to the carbonating reactor and thetemperature of the reaction mixture was adjusted to the desired startingtemperature of 20° C.

Before the start of carbonation, 30 kg of 10% w/w aqueous solution ofmagnesium sulphate (MgSO₄.7H₂O) was added to the milk of lime.

The agitator was then adjusted to 1480 rpm, and the slurry wascarbonated by passing a gas mixture of 26 volume percent carbon dioxidein air at 118 Nm³/h, corresponding to 19.7 litres per minute at standardtemperature and pressure per kilogram of calcium hydroxide, through theslurry.

During carbonation, 100 kg of 10% w/w aqueous solution of zinc sulphate(ZnSO₄.7H₂O) and 30 kg of 10% w/w aqueous solution of sulphuric acidwere added continuously to the reaction mixture over the totalcarbonation time.

Completion of carbonation was reached after 1 hour, 43 minutes reactiontime and indicated by a drop in conductivity to a minimum accompanied bya drop in pH to a constant value below 8.0.

During carbonation, the slurry temperature was allowed to rise resultingin a final slurry temperature of 62° C. due to the heat generated duringthe exothermic reaction.

The slurry was then screened on a 45 μm screen and the product recoveredas an aqueous slurry of the pigment.

The product of the carbonation step described above was an aqueoussuspension with 13.7% w/w solids content of ultrafine primary calciumcarbonate particles bound together to form stable porous sphericalaggregates.

The single crystals as constituents of the aggregates featured acicularparticle shapes with a diameter of 20 to 50 nm and aspect ratios between1:2 and 1:10.

The porous aggregates formed from these single crystals showed diametersbetween 1 and 5 μm, with an average diameter of 2 μm.

The crystalline structure of the product was determined by SEM pictures.

Pigment data of the product obtained in the process described above arelisted as Example 7 in Table 2.

These results call for the same comments as for Example 1.

Example 8 Process of the Invention, Upconcentration (Steps B) of theProduct of Example 7

10 litres of the precipitated calcium carbonate slurry obtainedaccording to the process described in Example 7 were screened on a 45 μmscreen prior to being fed to a thermal evaporator. The evaporatorconsisted of a cylindrical stainless steel vessel equipped with anagitator and a double mantle heating unit operating with 120° C. hotsynthetic oil as heating media.

Thermal upconcentration was achieved without dispersant throughevaporation in said lab evaporator under atmospheric pressure at slurrytemperatures ranging from 90 to 95° C.

The evaporation was stopped when the Brookfield viscosity reached adefined maximum limit of approximately 1000 mPas.

The product of the upconcentration process described above was anaqueous suspension with 27.1% w/w solids content of ultrafine primarycalcium carbonate particles, bound together to form stable porousspherical aggregates.

The crystalline structure of the product was determined by SEM pictures.

Pigment data of the product obtained in the process described above arelisted as Example 8 in Table 2.

Example 9 Process of the Invention, PCC Production (Step A, OptionMagnesium Sulphate and Zinc Sulphate) and Upconcentration (Steps B)

115 kg of quicklime were added to 1000 litres of tap water in a stirredreactor. Before lime addition, the water temperature was adjusted to 40°C.

The quicklime was slaked for 25 minutes under continuous stirring andthe resulting slurry of calcium hydroxide (“milk of lime”) at 13.5% w/wsolids was then screened on a 100 μm screen.

The calcium carbonate precipitation was conducted to a 1000 litrebaffled cylindrical stainless steel reactor equipped with an gasingagitator featuring a gas dispersion unit, a stainless steel carbonationtube to direct a carbon dioxide/air gas stream to the impeller, andprobes for monitoring the pH and conductivity of the suspension.

700 litres of the calcium hydroxide suspension obtained in the slakingstep as stated above, were added to the carbonating reactor and thetemperature of the reaction mixture was adjusted to the desired startingtemperature of 20° C.

Before the start of carbonation, 30 kg of 10% w/w aqueous solution ofmagnesium sulphate (MgSO₄.7H₂O) was added to the milk of lime.

The agitator was then adjusted to 1480 rpm, and the slurry wascarbonated by passing a gas mixture of 26 volume percent carbon dioxidein air at 118 Nm³/h, corresponding to 19.7 litres per minute at standardtemperature and pressure per kilogram of calcium hydroxide, through theslurry. During carbonation, 100 kg of 10% w/w aqueous solution of zincsulphate (ZnSO₄.7H₂O) and 30 kg of 10% w/w aqueous solution of sulphuricacid were added continuously to the reaction mixture over the totalcarbonation time.

Completion of carbonation was reached after 1 hour, 44 minutes reactiontime and indicated by a drop in conductivity to a minimum accompanied bya drop in pH to a constant value below 8.0.

During carbonation, the slurry temperature was allowed to rise resultingin a final slurry temperature of 56° C. due to heat generated during theexothermic reaction.

The slurry was then screened on a 45 μm screen.

Upconcentration Step:

The screened slurry was then fed at a rate of 400 l/h to a dewateringcentrifuge operating at 4440 rpm. No dispersant was added to theupconcentrated filtercake discharged by the dewatering centrifuge.

The mixture was then redispersed in a mixing unit and the upconcentratedproduct was recovered as an aqueous slurry of the pigment.

The product of the carbonation and upconcentration steps described abovewas an aqueous suspension with 24.9% w/w solids content of ultrafineprimary calcium carbonate particles, bound together to form stableporous spherical aggregates. The single crystals as constituents of theaggregates had acicular particle shape with a diameter of 20 to 50 nmand aspect ratios between 1:2 and 1:10. The porous aggregates formedfrom these single crystals showed diameters between 1 and 5 μm with anaverage diameter of 2 μm.

The crystalline structure of the product was determined by SEM pictures.

Pigment data of the product obtained in the process described above arelisted as Example 9 in Table 2.

Example 10 Process of the Invention, PCC Production (Step A, OptionMagnesium Sulphate and Aluminium Sulphate)

150 kg of quicklime were added to 1300 litres of tap water in a stirredreactor. Before lime addition the water temperature was adjusted to 40°C.

The quicklime was slaked for 25 minutes under continuous stirring andthe resulting slurry of calcium hydroxide (“milk of lime”) at 12.9% w/wsolids was then screened on a 100 μm screen.

The calcium carbonate precipitation was conducted in a 1000 litrebaffled cylindrical stainless steel reactor equipped with an gasingagitator having a gas dispersion unit, a stainless steel carbonationtube to direct a carbon dioxide/air gas stream to the impeller andprobes for monitoring the pH and conductivity of the suspension.

700 litres of the calcium hydroxide suspension obtained in the slakingstep as stated above were added to the carbonating reactor and thetemperature of the reaction mixture was adjusted to the desired startingtemperature of 20° C.

Before start of carbonation 30 kg of 10% w/w aqueous solution ofMgSO₄.7H₂O was added to the milk of lime.

The agitator was then adjusted to 1480 rpm, and the slurry wascarbonated by passing a gas mixture of 26 volume percent carbon dioxidein air at 100 Nm³/h through the slurry. During carbonation 100 kg of 10%w/w aqueous solution of Al₂(SO₄)₃.18H₂O and 30 kg of 10% w/w aqueoussolution of sulphuric acid were added continuously over totalcarbonation time to the reaction mixture.

Completion of carbonation was reached after 1 hour, 46 minutes reactiontime and indicated by drop in pH to a constant value below 8.0.

During carbonation slurry temperature was allowed to rise resulting in afinal slurry temperature of 56° C. due to heat generated in theexothermic reaction. The precipitated calcium carbonate was thenscreened on a 45 μm screen and the screened product was recovered as anaqueous slurry of the pigment.

Product of the carbonation step as stated above was an aqueoussuspension with 13.8% w/w solids content of ultrafine primary calciumcarbonate particles bond together to form stable porous sphericalaggregates. The single crystals as constituents of the aggregates hadacicular particle shape with a diameter of 20 to 50 nm and aspect ratiosbetween 1:2 and 1:10. The porous aggregates formed from these singlecrystals showed diameters between 1-5 μm with an average of 2 μm.

The crystalline structure of the product was determined by SEM pictures.

Pigment data of the product obtained in the process described above arelisted as Example 10 in Table 3.

Example 11 Process of the Invention, PCC Production (Step A, OptionMagnesium Sulphate and Aluminium Sulphate) and Upconcentration (Steps B)

500 litres of the precipitated calcium carbonate slurry obtainedaccording to process described in Example 10 was screened on a 45 μmscreen and the screened product was fed to a thermal evaporator.

Thermal upconcentration was achieved with no dispersant throughevaporation under −700 to −800 mbar vacuum at product temperaturesranging from 50 to 80° C.

The evaporation was stopped when Brookfield viscosity reached definedmaximum limit of approximately 1000 mPas.

Product of this upconcentration process as stated above was an aqueoussuspension with 28.1% w/w solids content of ultrafine primary calciumcarbonate particles bond together to form stable porous sphericalaggregates.

The crystalline structure of the product was determined by SEM pictures.

Pigment data of the product obtained in the process described above arelisted as Example 11 in Table 3.

Example 12 Process of the Invention, PCC Production (Step A, OptionMagnesium Sulphate and Aluminium Sulphate) and Upconcentration (Steps B)

1000 g of the precipitated calcium carbonate slurry obtained accordingto process described in Example 10 were added in a 2 litre stainlesssteel vessel. To the 1000 g pigment slurry 19 g of a 20% w/w solution ofcationic dispersant and 1 g of Hydroxy Ethyl Cellulose (HEC) were addedand mixed in under continuous stirring.

The mixture was then put on a heating plate for thermal upconcentrationvia evaporation.

The evaporation was stopped when Brookfield viscosity reached definedmaximum limit of approximately 1000 mPas.

Product of this upconcentration process as stated above was an aqueoussuspension with 21.3% w/w solids content of ultrafine primary calciumcarbonate particles bond together to form stable porous sphericalaggregates.

The crystalline structure of the product was determined by SEM pictures.

Pigment data of the product obtained in the process described above arelisted as Example 12 in Table 3.

In Tables 2 and 3, specific surface area (SSA) was measured using aTristar 3000 Analyzer, particle size distribution (PSD) using a HelosSympatec, brightness using a Datacolor Elrepho 3000 Jerics, solidscontent using a Mettler Toledo HB43 Halogen balance, and viscosity usinga Brookfield DVII Viscometer, all according to the recommendations ofthe manufacturer.

TABLE 2 Characteristics of the Pigments and Pigment-Containing Slurriesof the Invention Test Unit Example 1 Example 2 Example 3 Example 4Example 5 Example 6 Example 7 Example 8 Example 9 BET Specific m2/g 58.960.1 56.4 63.5 59.5 62.3 75.2 65.5 74.2 Surface Area PSD (HelosSympatec) <2 μm % 31 35 33 33 16 18 12 18 17 <1 μm % 8 9 8 10 5 10 4 6 5Average μm 2.72 2.60 2.57 2.65 3.73 2.62 4.25 3.95 4.01 particlediameter d50 Brightness (DIN 53140) R457 (ISO % 96.1 95.5 94.6 95.6 95.795.6 95.6 94.9 95.5 2469) Yellow index 1.5 1.4 1.5 1.5 1.6 1.4 1.6 1.51.5 (DIN 6167) Solids content % 15.6 28.4 22.5 19.5 14.3 23.8 13.7 27.124.9 Viscosity mPas 34 1300 840 460 33 745 22 782 850

TABLE 3 Characteristics of the Pigments and Pigment-Containing Slurriesof the Invention Test Unit Example 10 Example 11 Example 12 BET Specificm2/g 63.5 60.8 41.9 Surface Area PSD (Helos Sympatec) <2 μm % 37 37 45<1 μm % 11 10 11 Average particle μm 2.45 2.43 2.16 diameter d50Brightness (DIN 53140) R457 (ISO 2469) % 95.7 94.6 94.7 Yellow index(DIN 1.4 1.5 1.9 6167) Solids content % 13.8 28.1 21.3 Viscosity mPas 351370 604

Coating Trials

A selection of the above products of the invention were introduced inpaper coating slurries and coated onto paper.

Coating Trials Based on Example 3, 9, 11 and 12 Slurries on a K-Coaterwith a Grooved RodCoating formulation:

Four paper coating slurries were prepared, each using one of four PCCslurries prepared according to the invention, along with standardadditives for Varibar coating. These additives (Mowiol 26-88, Printofix,Cartafix VXT01 and Cartabond TS1) were obtained from Clariant.

TABLE 4 Coating formulation compositions (by parts) Solids content (%Coating Coating Coating Coating Coating Slurry w/w) Slurry 1 Slurry 2Slurry 3 Slurry 4 Example 3 22.5 100 Example 9 24.9 100 Example 11 28.1100 Example 12 21.3 100 Additives Mowiol 26-88 7.6 12 12 12 12 Printofix43.0 5 5 5 5 Cartafix VXT01 20.0 3 3 3 3 Cartabond TS1 43.0 1.5 1.5 1.51.5 Final slurry characteristics Final slurry pH % 8.1 8.2 8.2 8.0 Finalslurry solids — 27.8 27.8 27.8 27.8 content Final slurry Brookfield mPas140 220 300 100 viscosity at 20° C.

TABLE 5 Base Paper Characteristics, Coating Slurries 1-4 Grammage 89.2g/m² Filler content (otro)  12.9% Tension length 5.26 km Surface contactangle OS (1σ) 109.3 Surface contact angle OS (10σ) 106.4 Yellow index OS−18.3%

TABLE 6 Coating Machine Conditions on a K-Coater with a grooved rodCoating application weight 8 g/m² Coating Moisture content 5% Coatingcolour temperature during 23° C. coating Paper drying conditions Driedin a lab oven at 80° C. for 4 minutes

Coating the base paper with Coating Slurries 1 to 4 lead, respectively,to Coating Trial 1 to 4 results below.

Ink Jet Printing Trials

Printing trials were conducted on the same three different inkjetprinters as previously, namely the Epson Stylus Photo 950, the HPDeskjet 5550 and the Canon i950. The test card was designed to assessthe optical density, as well as the degree of feathering and bleeding.

The HP Bright White paper is marketed as a multipurpose inkjet papers.The Zweckform 2585 and Epson S041061 papers are considered to representhigh quality matt inkjet papers, offering a higher print quality thanstandard multipurpose inkjet papers.

Optical density was measured using the Gretag D 186 densitometeraccording to the standard procedures indicated by the manufacturer. Foran equal quantity of applied ink, the higher the optical density, thebetter the coating maintains the dyes on the paper surface.

Papers Coated with Coating Slurries 1 to 4:

Bleeding and feathering were measured using the Personal IAS® (ImageAnalysis System) instrumentation from Quality Engineering Association,Inc., according to the standard procedures given by the manufacturer.The lower the measured value, the better the bleeding and feathering.

TABLE 7 Optical Density and Bleeding/Feathering Results of Paper Coatedwith the Coating Pigment of the Invention, as Opposed to Market PapersOptical density Gretag-Macbeth D186 Printer type cyan magenta yellowGreen, Blue, m Red, y Epson stylus black black (c), (m) (y), c 100% 100%100% photo 950 100% 80% 100% 100% 100% y 100% c 100% m 100% BleedingFeathering Zweckform 2585 2.38 1.29 2.25 1.64 1.54 1.66 2.04 1.55 164.1458.00 Epson S041061 2.45 1.23 2.09 1.59 1.49 1.54 1.85 1.51 166.34 67.63HP Bright White 2.09 1.06 1.72 1.42 1.34 1.32 1.61 1.31 239.20 104.37Coating Trial 1 2.40 1.21 2.13 1.49 1.51 1.60 2.01 1.49 172.49 72.01Coating Trial 2 2.38 1.19 2.09 1.45 1.48 1.55 1.94 1.42 185.32 63.89Coating Trial 3 2.40 1.23 2.15 1.52 1.48 1.67 2.13 1.52 167.20 62.45Coating Trial 4 2.27 1.17 2.11 1.42 1.42 1.46 1.79 1.38 198.45 79.55

The above table shows that the optical density obtained with the productof the invention approaches the quality of a superior inkjet paper. Thebleeding obtained with the product of the invention is equal or inferiorto other equivalent market papers. The feathering obtained with theproduct of the invention is inferior to other market papers.

The improved optical density, bleeding and feathering attest to animproved balance of absorption/adsorption properties relative tocompeting market products.

TABLE 8 Optical Density and Bleeding/Feathering Results of Paper Coatedwith the Coating Pigment of the Invention, as Opposed to Market PapersOptical density Gretag-Macbeth D186 Printer type cyan magenta yellowGreen, Blue, m Red, y HP Deskjet black black (c), (m) (y), c 100% 100% c100% m 5550 100% 80% 100% 100% 100% y 100% 100% 100% Bleeding FeatheringZweckform 2.08 1.16 0.98 1.00 1.46 1.20 1.84 1.38 194.21 63.94 2585Epson 1.92 1.09 0.97 0.97 1.47 1.18 1.73 1.47 193.69 66.95 S041061 HPBright 2.35 1.24 1.02 1.01 1.39 1.17 1.59 1.33 237.72 72.59 WhiteCoating Trial 1 2.11 1.20 0.97 0.99 1.43 1.16 1.80 1.36 233.55 64.45Coating Trial 2 2.09 1.29 0.92 0.89 1.34 1.18 1.76 1.38 199.34 76.44Coating Trial 3 2.37 1.19 1.03 0.99 1.45 1.21 1.81 1.49 212.64 66.87Coating Trial 4 2.15 1.11 0.89 0.93 1.39 1.12 1.65 1.37 214.11 67.79

The optical density results of the invention were superior to comparablemarket papers. A decreased bleeding and an increase in featheringrelative to comparable papers were also noted.

TABLE 9 Optical Density and Bleeding/Feathering Results of Paper Coatedwith the Coating Pigment of the Invention, as Opposed to Market PapersOptical density Gretag-Macbeth D186 cyan magenta yellow Green, c Blue, mRed, y Printer type black black (c), (m) (y), 100% y 100% 100% Canoni950 100% 80% 100% 100% 100% 100% c 100% m 100% Bleeding FeatheringZweckform 2.07 1.20 2.30 1.74 1.71 1.58 2.31 1.85 198.63 59.64 2585Epson 2.06 1.17 2.06 1.80 1.66 1.42 1.82 1.68 204.45 63.72 S041061 HPBright 1.72 1.03 1.73 1.58 1.49 1.26 1.58 1.46 245.32 90.74 WhiteCoating Trial 1 1.98 1.15 2.12 1.74 1.63 1.49 1.76 1.55 209.13 83.70Coating Trial 2 1.85 1.07 2.01 1.56 1.60 1.31 1.81 1.61 222.65 85.67Coating Trial 3 2.01 1.19 2.11 1.73 1.69 1.55 2.11 1.62 207.83 62.89Coating Trial 4 1.77 1.11 1.79 1.66 1.68 1.50 2.01 1.57 217.44 72.47

The optical density results of the invention approached the values givenby superior quality papers. A decreased bleeding and similar degree offeathering relative to comparable market papers was noted.

The present invention also covers the technical equivalents of the abovedescription, as well as options that would be easily available to theskilled man when reading the present application.

1. Process for providing PCC useful for ink-jet printing applications,of the type according to which a calcium hydroxide slurry is firstprepared by mixing quicklime (CaO) with water in a stirring reactor ortank (“slake”), the calcium hydroxide slurry is then screened, such ason a 100 μm screen, to remove any residual impurities and/ornon-reactive unburnt lime, the screened slurry is then directed towardsa stainless steel reactor equipped with an agitator; the temperature isadjusted, generally to between 10 and 70° C., and subsequently theslurry is directed towards a carbonation reactor or tank, wherein carbondioxide-containing gas is bubbled through the slurry, the slurry exitsthe carbonation tank when appropriate in view of conductivity and pH,generally when the conductivity reaches a minimum and the pH drops below8, coarse particles are removed on a screen, such as a 45 μm screen,such that the slurry contains only the ultrafine PCC agglomerates of theinvention, characterized by the implementation of process stepscomprising the following: A First steps, production of the PCC: A1 thecarbonation step is performed at a carbonation gas flow rate of below 30litres per minute at standard temperature and pressure per kilogramcalcium hydroxide during precipitation.
 2. Process according to claim 1,characterized in that A2 the slurry of calcium hydroxide leaving saidstainless steel reactor after said separation of said residualimpurities and/or non-reactive unburnt lime is treated by a combinationof magnesium sulphate and Group II and/or Group III metal sulphates mostpreferably in the presence of an acid said acid being most preferablysulphuric acid until stable, porous agglomerates/aggregates are obtainedat a concentration of 5 to 25% solids, preferably 15 to 20% solids(“precursor”).
 3. Process according to claim 1, characterized in that A3said slurry of calcium hydroxide is first prepared by mixing quicklimewith water in a stirring reactor or tank (“slake”) in a weight ratio ofCaO:water between 1:3 and 1:20, preferably between 1:5 and 1:12, mostpreferably between 1:7 and 1:10.
 4. Process according to claim 1,characterized in that A4 the temperature is preferably adjusted tobetween 15 and 50° C., most preferably to between 15 and 30° C., beforethe slurry is directed towards the carbonation reactor or tank. 5.Process according to claim 1, characterized in that Steps A are followedby the following steps, Steps B: B Upconcentration of the “precursor”:dewatering/redispersing steps following the above “Steps A”upconcentration of the PCC produced during Steps A is performed undersufficiently gentle or mild conditions for the aggregates/agglomeratesnot to be substantially destroyed, said upconcentration is conductedwithout the use of a dispersing aid or with a cationic dispersing aid,and the amount of any cationic dispersant added is controlled so thatthe PCC agglomerates/aggregates of the precursor are just coated, thisquantity corresponding that added prior to a slurry viscosity increase,until a concentration of 15 to 50%, preferably in the range 20 to 30%,most preferably 23 to 26% solids by weight is reached.
 6. Processaccording to claim 1, characterized in that in Steps A one applies atleast one of the following parameters: the carbonation gas flow rate ispreferably selected in the range of 1 to 30, preferably 10 to 20, mostpreferably around 19.7 litres per minute at standard temperature andpressure per kilogram calcium hydroxide during precipitation, saidcarbonation gas is CO₂ or a mixture of CO₂ and one or more other gases,such as air and/or nitrogen, the slurry of calcium hydroxide is mostpreferably treated by a combination of magnesium sulphate and aluminiumsulphate, or a combination of magnesium sulphate and zinc sulphate. 7.Process according to claim 1, characterized in that in Steps A oneapplies at least one of the following parameters: zinc sulphate can beadded to the combination of magnesium sulphate and aluminium sulphate,aluminium sulphate can be added to the combination of magnesium sulphateand zinc sulphate, the addition of magnesium sulphate is most preferablyperformed before carbonation, magnesium sulphate can be added, in a lesspreferred option, either before the addition of other sulphates orduring that addition, magnesium sulphate can be added, as a lesspreferred option, during carbonation along with aluminium and/or zincsulphate, magnesium sulphate can be added during carbonation or at thebeginning of carbonation, the addition of aluminium sulphate and/or zincsulphate takes place during carbonation, the addition of the acid,namely sulphuric acid, most preferably under the form of a 10% by weightsolution of H₂SO₄, takes place at the beginning of carbonation mostpreferably, the addition of H₂SO₄ takes place simultaneously with theaddition of aluminium or zinc sulphate, in all the above options,sulphates of Group II and/or III can be added in addition to aluminiumand/or zinc sulphates, or as a substitute for aluminium and/or zincsulphates, the temperature in the carbonation tank is observed to riseup to between 40 to 80° C., preferably up to between 50 to 60° C., mostpreferably up to between 56 and 57° C., removal of residual impuritiesand/or non-reactive unburnt lime takes place on a 45 μm mesh screen whenthe Brookfield viscosity of the material exiting the carbonation tank issufficiently low, namely less than 100 mPas at 100 rpm, the final slurryproduct substantially consists of stable, porousagglomerates/aggregates.
 8. Process according to claim 1, characterizedin that in Steps B, by “gentle or mild conditions” it is meant that thedeagglomeration/deaggregation of the agglomerates/aggregates is kept toa minimum so that said agglomerates/aggregates are not “substantiallydestroyed”, that is, during the upconcentration steps: the increase ofthe fraction of particles below 2 μm is limited to less than 30%,preferably less than 20%, most preferably less than 10%, and/or thedecrease of the mean aggregate diameter is limited to less than 20%,preferably less than 15%, most preferably less than 10%, as measuredusing a Helos apparatus, by “deagglomeration/deaggregation” it is meantthat the agglomerates/aggregates obtained at the end of Steps A by thespecific process of the invention are disintegrated, the upconcentrationstep can be performed in the form of any thermal or mechanicalseparation technology for solid/liquid suspensions provided theaggregates/agglomerates obtained in Steps A (“precursor”) aresufficiently stable and are not “substantially destroyed” by saidtechnology.
 9. Process according to claim 1, characterized in that: theupconcentration is performed in a centrifuge, or a pressurized filter,or vacuum filtration or by thermal upconcentration, without dispersantor in the presence of a cationic dispersant, and characterised in thatthe final slurry concentration is about 23 to 26% solids by weight. 10.Process according to claim 1, characterized in that the upconcentrationleads to a filter cake, such as by upconcentrating in a pressurizedfilter or in a centrifuge or by vacuum filtration, and in such a case:the concentrated material is optionally washed with water a redispersionis performed until the final material substantially consists of stable,porous agglomerates/aggregates, the upconcentration can be performed ina thermal evaporation step with the final material substantiallyremaining under the form of the stable, porous agglomerates/aggregates.11. Process according to claim 5, characterized in that theupconcentration of part or all of the precursor leads to a dry product,and in such a case: a redispersion is performed until the final materialsubstantially consists of stable, porous agglomerates/aggregates. 12.Process according to claim 6, characterized in that approximately 5 to9% w/w of a cationic dispersant, such as a cationic copolymer of[2-(methacryloyloxy)ethyl]trimethyl ammonium chloride and[3-(methacrylamido)propyl]trimethyl ammonium chloride, relative to drycalcium carbonate, along with HEC, is added to the slurry.
 13. Processaccording to claim 5, characterized in that the final slurryconcentration is partially or wholly obtained by the addition of one ormore additional pigments or pigment slurries during Steps B.
 14. Stable,porous aggregates/agglomerates of PCC characterized in that they havebeen obtained according to claim
 1. 15. Stable, porousaggregates/agglomerates of PCC characterized in that they feature thefollowing properties: a specific surface area of 30 to 100 m²/g,preferably from 50 to 80 5 m²/g, and/or a mean aggregate diameter of 1to 5 μm, with an average diameter of 2 μm, and/or a fraction of finesbelow 2 μm of less than 20%, preferably less than 15% (as measured on aHelos Sympatec), and/or a primary particle size of the acicularparticles of 20 to 50 nm with an aspect ratio between 1:2 and 1:10and/or a solids content, by weight from 5 to 25%, preferably 15 to 20%at the end of Steps A, and a solids content of 15 to 50%, preferably 20to 30%, in particular 23 to 26% solids at the end of Steps B.
 16. Novelpigments characterized in that they comprise stable, porous PCCaggregates/agglomerates according to claim
 14. 17. Novel pigment or PCCslurries characterized in that they comprise stable, porous PCCaggregates/agglomerates according to claim
 14. 18. Novel pigments or PCCslurries according to claim 17, characterized in that their solidsconcentration is, by weight: when in the form of the “precursor” at theend of Steps A, from 5 to 25%, preferably from 15 to 20% solids when inthe form of the final upconcentrated PCC (Steps B), from 15 to 50%solids, preferably from 20 to 30% solids, in particular from 23 to 26%solids.
 19. Coating formulations for the paper making industrycharacterized in that they comprise novel aggregates/agglomerates ofPCC, novel pigments and/or novel slurries according to claim
 16. 20.Coating formulations according to claim 19 characterized in that the PCCslurry which it contains features the following properties a solidscontent from 15 to 50%, preferably 20 to 30, in particular around 23 to26%/weight, and/or a high specific surface area PCC, with a specificsurface area of 30 to 100 m²/g, preferably from 50 to 80 m²/g. 21.Applications of the coating formulations according to claim 19 to thecoating of inkjet paper, namely for specialty or high-quality ink jetpaper.
 22. Applications of the coating formulations according to claim19 to the coating of matt inkjet paper.
 23. Inkjet paper, namelyspecialty or high-quality ink jet paper, namely matt inkjet paper,characterized in that it is coated with at least one coating compositionaccording to claim 19.